Superparamagnetic relaxation time of a single-domain particle with a nonaxially symmetric double-well potential

The analytical estimates for the relaxation time of a single-domain particle with a nonaxially symmetric double-well potential are obtained in the limits of low and high dissipation regimes. The expressions derived turn out to be valid also for an important case of spheroidal nanoparticle whose easy anisotropy axis is inclined at an arbitrary angle to a shape anisotropy axis. The analytical estimates are compared with the numerical simulation results obtained for the same particle by means of solution of the stochastic Landau-Lifshitz equation at various values of the dimensionless damping parameter kappa. It is shown that in the case of moderate reduced energy barrier the high damping limit occurs at kappa >= 1.0, whereas the low damping limit corresponds to very small values of the damping parameter, kappa <= 0.003. For intermediate values of kappa, a heuristic interpolation formula for the particle relaxation time is suggested. It describes the numerical simulation results with accuracy of several percent.